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Low Emittance Generation and Preservation: Damping Rings

Low Emittance Generation and Preservation: Damping Rings. Y. Papaphilippou (CERN) and J. Urakawa (KEK). October 23 rd , 2012. ILC Damping Ring Layout. Problems come from electron cloud and fast ion instability. Regarding with bunch-by-bunch extraction, we have to

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Low Emittance Generation and Preservation: Damping Rings

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  1. Low Emittance Generation and Preservation: Damping Rings Y. Papaphilippou (CERN) and J. Urakawa (KEK) October 23rd, 2012

  2. ILC Damping Ring Layout Problems come from electron cloud and fast ion instability. Regarding with bunch-by-bunch extraction, we have to make a careful beam optical matching and a smooth impedance design. This issue was already confirmed by ATF extraction beam tuning(10pm, not 2pm. ) Wiggler RF Phase Trombone EmittancePreservation in ILC Damping Ring Chicane Extraction Injection

  3. DTC lattice parameters for 5 Hz Low Power (baseline) and High Luminosity (upgrade) operating modes and 10 Hz repetition rate (baseline) operation Three ILC operating modes correspond to four DR configurations, Two utilize a 5 Hz repetition rate: low power baseline (1312 bunches/ring); and high luminosity upgrade (2625 bunches. Third operating mode is at 10 Hz and e- linac operated with alternating pulses: high energy for e+ production followed by low energy for collisions. Shorter damping times in necessary to achieve the same extracted vertical emittance in half the nominal storage time

  4. Damping Ring Arc Magnet Layout Doubling of current in e+ DR for high luminosity upgrade poses concern for electron cloud effects. If mitigation techniques are not sufficient, possibility of installing a second e+ ringin the same tunnel.

  5. Arc Cell and Damping Ring Lattice Functions

  6. BPM, Magnet Alignment Tolerances and Dynamic Aperture, Specified Geometric Vertical Emittance of 2pm-rad

  7. Electron Cloud Mitigations and Modeling Results Measurements in CESRTA, simulations with several codes for various bunch configurations, chamber geometries and coatings (ILC e-cloud WG). Recommendations for mitigations include coating, grooves, clearing electrodes, solenoids and antechambers

  8. Fast Ion Instability in Electron Damping Ring Simulation Codes based on week strong model predict confirmed by Experimental result very fast rise of vertical emittance due to FII. Growth rate reduced when introducing train mini-gaps

  9. Simulated Vertical Amplitude versus time due to Fast Ion Instability Simulation Codes confirmed by experimental results at ATF-DR, CesrTA, SPEAR3 and low emittance SR Rings predict that fast ion instability can be mitigated with good vacuum level less than 1nT, many train operation with train gap and b-by-b feedback system.

  10. Vacuum System

  11. Extraction Kicker Very tight kicker jitter tolerance performance (<5e-4) confirmed in ATF experimental results (single bunch extraction for train of 10 bunches with spacing of 5.6 ns). Need to address impedance issues for 42 strip-line kickers (30cm long, 30mm gap)

  12. e- linac to PDR transfer line X-ray dump e- Pre-damping Ring X-ray dump X-ray dump e- PDR to DR transfer line e- Damping Ring X-ray dump e- DR to Booster linac transfer line CLIC Damping Rings Complex layout Delay loop e+ DR to Booster linac transfer line X-ray dump e+ Damping Ring e+ PDR to DR transfer line X-ray dump X-ray dump e+ Pre-damping Ring X-ray dump e+ linac to PDR transfer line

  13. CLIC DRchallenges and adopted solutions • High-bunch density in all three dimensions • Intrabeam Scatteringeffect reduced by choice of ring energy, lattice design, wiggler technology and alignment tolerances • Electron cloud in e+ ring mitigated by chamber coatings and efficient photon absorption • Fast Ion Instability in the e- ring reduced by low vacuum pressure and large train gap • Space charge vertical tune-shift limited by energy choice, reduced circumference, bunch length increase • Other collective instabilities controlled by low –impedance requirements on machine components • Repetition rate and bunch structure • Fast damping times achieved with SC wigglers • RF frequency reduction @ 1GHz considered due to many challenges @ 2GHz (power source, high peak and average current, transient beam loading) • Output emittance stability • Tight jitter tolerance driving kicker technology • Positron beam dimensions from source • Pre-damping ring challenges (energy acceptance, dynamic aperture) solved with lattice design LCWS2012

  14. CLIC DR layout and parameters • Racetrack shape with • 96 TME arc cells (4 half cells for dispersion suppression) • 26 Damping wiggler FODO cells in the long straight sections (LSS) • Space reserved upstream the LSS for injection/extraction elements (optics design ready) and RF cavities • Circumference reduced (30% less wigglers) LCWS2012

  15. Intrabeam Scattering theory, simulations and measurements • Energy choice and lattice design for reducing effect from IBS • Monte-Carlo tracking codes developed based on Ratherford Coulomb scattering cross section • Code agreement for lower currents, more divergence at high currents • First measurements at SLS-PSI with good agreement with theoretical predictions 1mA, 10mA, 17mA F. Antoniou, et al. LCWS2012

  16. Other collective effects E. Koukovini-Platia, G. Rumolo, et al. • Space-charge reduced <0.1 with combined circumference reduction and bunch length increase • e-cloud in the e+ DR imposes limits in PEY (99.9%) and SEY (<1.3) achieved with wiggler absorption scheme and chamber coatings (amorphous carbon) • Fast ion instability in e- DR constrains vacuum pressure to around 0.1nTorr (large train gap also helps) • Single bunch instabilities avoided with smooth vacuum chamber design • Simulations for instability thresholds for resistive wall • Resistive wall coupled bunch controlled with feedback • Conceptual design of 1-2GHz b-b-b feedback by T. Nakamura (SPring8) • Impedance estimates for effect of multiple material layers • Coherent synchrotron radiation estimates do not

  17. Wigglers’ effect with IBS • Stronger wiggler fields and shorter wavelengths necessary to reach target emittance due to strong IBS effect • Stronger field and moderate wavelength reduces IBS effect while reaching target emittance • Current density can be increased by different conductor type • Nb3Sn can sustain higher heat load (~10 times higher than NbTi) • Two wiggler mock-ups • 2.5T, 5cm period NbTi(CERN/BINP) • 2.8T,4cm period, Nb3Sn (CERN) • Magnetically tested achieving required performance F. Antoniou LCWS2012 500nm limit

  18. SC wiggler development A. Bernard, P. Ferracin, N. Mesentsev, D. Schoerling, et al. • Two paths of R&D • NbTi wire, horizontal racetrack, conduction cooled (BINP/KIT collaboration) • Nb3Sn wire, vertical racetrack, conduction cooled (CERN) • Full NbTilength prototype • Higher than 3T, 5.1cm period, magnetic gap of 18mm • Under production by BINP to be installed in 2014 in ANKA for beam tests • Operational performance, field quality, cooling concept • First vertical racetrack magnet (3-period) tested in 2011 • Reached 75% of max. current • Limited by short coil-to-structure • Still higher than NbTi (900 A vs. 700 A) LCWS2012

  19. Vacuum technology S. Calatroni, M.Palmer, G. Rumolo, M. Taboreli et al. • Amorphous-C coating shows maximum SEY starting from below 1 and gradually growing to slightly more than 1.1 after 23 days of air exposure • Peak of the SEY moves to lower energy • Experimental tests • Huge amount of data at SPS • Run with 5 GeVpositrons at CESRTA, for different intensities and bunch spacings • The total electron current reduced significantly (1 order of magnitude) as compared to Al • Continuing collaboration with ESRF for PEY tests in a dedicated beamline 15W is a C-coated chamber 15E is an Al chamber Factor 4 less electron flux, to be multiplied by a factor 2 difference of photoelectron in 15W wrt 15E LCWS2012

  20. A. Grudiev RF system • Single train of 312 bunches spaced at 0.5ns necessitates 2GHz system • R&D needed for power source • Large average and peak current/power introduces important transient beam loading • Considered 1GHz system • Straight-forward RF design but train recombination in a delay loop is needed

  21. Extraction kicker design M. Barnes, C. Belver- Aguilar, A. FausGolfe et al. Inductive Adder • Kicker jitter tolerance ~ few 10-4 • Striplines required for achieving low longitudinal coupling impedance • Significant R&D needed for PFL (or alternative), switch, transmission cable, feed-throughs, stripline, terminator • Prototyped under the Spanish Program “Industry for Science” • Collaboration is set-up with ALBA synchrotron and ATF for beam tests LCWS2012

  22. Reaching Quantum Limit Of Vertical Emittance M. Aiba et al, NIM 2012 • Tousheck lifetime vs. RF voltage in ASLS points to εy = 1.24 ± 0.3pm • New technique for resolving ultra-low beam sizes using vertical undulator K. Wootton, et al, PRL, accepted • EU collaboration between PSI-SLS (Maxlab), INFN-LNF and CERN (TIARA-SVET) for low emittance tuning techniques and instrumentation • SLS achieved εyrecord of 0.9 ± 0.4pm (confirmed with different techniques) • New emittance monitor for resolutions below 3μm (vertical polarized light) under installation for measurements in 2013

  23. DR technology and experimental program • Super-conducting wigglers • Demanding magnet technology combined with cryogenics and high heat load from synchrotron radiation (absorption) • High frequency RF system • 1-2GHz RF system in combination with high power and transient beam loading • Coatings, chamber design and ultra-low vacuum • Electron cloud mitigation, low-impedance, fast-ion instability • Kicker technology • Extracted beam stability • Diagnostics for low emittance • Profile monitors, feedback system • Experimental program set-up for measurements in storage rings and test facilities • ALBA (Spain), ANKA (Germany), ATF (Japan), Australia Synchrotron (Australia), CESRTA (USA), SOLEIL (France),… • Ideas for a DR test facility within a future LC test facility

  24. Low Emittance Rings’ Collaboration • Initiated by the ILC-CLIC working group on damping rings and catalyzed by the organization of two workshops (01/2010 @ CERN, 10/2011 @ Heraklion) • Common beam dynamics and technology items for synchrotron light sources, linear collider damping rings, b-factories • Formed a EU network within EUCARD2 • Coordinated by EU labs • Extended collaboration board including colleagues from US and Japan • 30 participating institutes world wide • Proposal approved with 330k€ allocated budget for 4 years starting 05/13 LCWS2012

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